The present disclosure relates to a compact portable device for the generation of concentrated respirable dry particles from an aqueous solution or suspension.
There is an ever increasing need to deliver large masses of biologics and other agents to the respiratory tract by aerosol. Many devices which generate liquid aerosols may not work well with molecules of high molecular weight or at high concentrations. In addition, some of these devices may degrade the molecules during aerosolization. These limitations, together with the need to reduce the use of fluorocarbons, have lead to the development of dry powder inhalers. In these devices a “blister” or capsule containing the drug is broken and the powdered drug together with the included excipients is dispersed using a vortex caused by inhalation or aerosolized by some other mechanical means such as sonication. Excipients are added to the active agent to aid in the aerosolization of these agglomerates. In some cases, such as Exhubra, they comprise some 70% of the mass of the mixture. The use of excipients results in increased formulation costs, safety pharmacology costs and potential unwanted side effects. These dry powers containing the active agent are most often generated using a spray-drying process. Spray driers have been in common use for many years. Generally they consist of generating an aerosol at the top of a vertical cylindrical tower in which the aerosol spray is diluted with warm gas that may be in the same direction as the spray or in the opposite direction. A cyclone at the output is used to collect the resulting powder. Excipients are added to the collected powders to aid in their dispersion. This mixture is placed in a dry power inhaler, DPI. There are several limitations with this approach:
a) The stored resultant dry particles must be stable and preferably resistant to high humidity.
b) They must be formulated with excipients such as to be easily dispersed
c) The size of the drug particles is generally smaller than that of the excipient particles when the two chemicals are in discrete form.
d) The maximum which can be inhaled is limited to the size of the capsule not the volume of the inhalation.
e) The spray dry process is likely 60% efficient and the delivery to the lungs by the dry power inhaler 30% efficient resulting in losses of some 80% of the active agent.
f) A rapid inhalation results in most of the powder in the capsule being aerosolized but results in high mouth and throat deposition. A slow inhalation can result in higher deep lung deposition but a low efficiency of aerosolization of the powder in the capsule. These issues lead to wide variability in the dose administered leading to both efficacy and safety concerns.
These issues can be overcome by a device which generates a liquid aerosol containing the active agent, dries it, concentrates and delivers the residual dry aerosol of the active agent to the lungs in one continuous set of processes such as described in this disclosure. It should be recognized that even the instruments which are of laboratory rather than commercial size are 70 in tall and weigh 50-80 kg. Of note, the spray towers in all these instruments are vertically orientated. A compact clinical device would be best served by a small horizontal drying chamber.
Delivery of higher masses to the lungs than can be obtained with solid particles of drug can be achieved with aerosols of the same aerodynamic diameter that have a particle density of less than 1 (Edwards 1996). The formulation of such particles have been the subject of a number of patents, including, U.S. Pat. No. 7,435,408). Large porous particles have been produced by spray drying a mixture of polyester and an active agent such as insulin. These spray dried aerosols have generally been produced by standard spray drying techniques and collected as a powder. To produce particles with a low density, a liquid which has a small molecular weight as compared to a much larger molecular weight additive in the solvent evaporates faster than the diffusion of the large molecular weight component. The resulting particles may be either hollow or have open gas spaces making the geometrical diameter larger than the aerodynamic diameter. These aerosols are generally collected using a cyclone. The powders so produced must later be reaerosolized to be inhaled by the patient. As noted, using such techniques only a small fraction of the original drug is delivered to the lungs. The present disclosure describes how the dilution of a plume of aerosol can be rapidly diluted near to its origin of formation using a heated counter-flow gas jet coaxial in opposite direction to that of the aerosol plume. In addition an annulus of dilution gas transports the aerosol away from the generator along an evaporation chamber to a virtual concentrator. The present disclosure also describes how the evaporation of these aqueous particles in this disturbed plume can be augmented by provision of infrared radiation from a source outside the evaporation chamber.
The U.S. non-provisional patent application Ser. No. 11/315,951 filed on Dec. 22, 2005 and published under the publication no. US-2007-0144514-A1 (Yeates et al.), the benefit of which is claimed for the present application, has described a dry power aerosol generator and processing system whereby aqueous solutions of agents are aerosolized, evaporated, concentrated and delivered as a dry power aerosol comprised entirely of the dissolved solute. In the present disclosure are described details of improvements to that system and the subsequent novel findings regarding the generation of pure protein respirable aerosols with a density less than one in a compact device. This device eliminates the need for spray-drying, collection with a cyclone, mixing with excipients and placing in a dry powder inhaler. The improvements to that system are detailed within, The marked reduction of internal gas flow resistance has enabled the use of a blower that is only 2×2×1 inch, thus increasing the portability of the device. Easy to assembly friction fit designs eliminated the use of large O-ring seals on the evaporation chamber making it much easier to assemble by a sick patient. Light weight heaters with resistance to flow as well as a low thermal inertia were developed to allow functionality within a minute of turning on and increase the portability. The counter-flow tube was centered within the concentrator to ensure easy assembly and accurate alignment with the axis of the aerosol jet thus increasing the reliability of its performance. An additional heating element for the warming of the gas for the nozzle and the counter-flow has been included enabling more rapid evaporation of the aerosol plume. Focusing reflectors have been included on the infrared heat source to lower the power needed for the infrared heater. This and the above modifications reduce the overall power used by the device. These and other functional and practical improvements have been disclosed herein. In concert they make the device more portable, more functional, easier and more cost effective to manufacture and provide new possibilities for the generation of novel particles for immediate inhalation that was not previously possible.
Virtual impaction has been used as a means to concentrate aerosols (U.S. Pat. No. 4,767,524, Pillai and Yeates, 1994). There have been several modifications of these designs, including the use of slit orifices in place of round orifices (Marple and Robow 1986), Yeates' patent application 200701445 uses this information to design a concentrator with radial slits for a cut-off diameter of 2.5 micron. The present disclosure shows how to concentrate the major mass of particles within the respiratory range. This range is typically 1-5 micron but may cover the range of 0.5-10 micron. According to Marple and Robow, to capture particles above 1 micron a 1 mm orifice slit is required compared to a 2.6 mm slit to concentrate particles above 2.5 micrometers. This potentially increases the pressure head required to accelerate the aerosol through the slits. To reduce the pressure head upstream of the concentrator, parabolic entrances to the orifices were incorporated into the design. It is notable that Seshadri, AAAR 2006, teaches the use of a parabolic entry profile together with a sheath gas flow to reduce wall losses and potentially enhance the concentration factor. As noted, in this present disclosure they are incorporated to reduce the upstream pressure required to operate the concentrator. Shekarrizz, U.S. Pat. No. 7,178,380 describes a concentrator with concave and convex accelerator walls together with a side injector port they claim reduces clogging. That concentrator utilizes input flow rates of 15 liters/minute, just a small fraction of the flow rates in the present device which are typically between 100 and 300 liters per minute but higher and lower flow rates are possible in this disclosed device. The present device does not have, nor does it require, the proposed injector ports to prevent clogging. Alternatively, U.S. Pat. Nos. 7,261,007 and 5,858,043 describe concentric slits to reduce end effects. When concentric slits are used it is much more difficult to exhaust the gas than using the present compact design.
A first object of the present disclosure is to provide the means, in a small practical device, to generate an aqueous (or other solvent with a high vapor pressure) aerosol and by dilution and heating, rapidly evaporate aqueous aerosols and thereafter to concentrate the resultant particles and deliver them at flow rates compatible with the full range of normal inspiratory flows.
A second object of the present disclosure is to eliminate high pressure couplings so the device can be easily assembled and disassembled for cleaning.
A third object of the invention is to lower the resistance to gas flow through the device to enable the construction of a small device using a small blower to provide the dilution gas.
A fourth object of the present disclosure is to minimize leakage of gas and/or aerosol between the various components of the device while maintaining structure integrity junction between each of the components.
A fifth object of the present disclosure is to facilitate the provision of a counter-flow gas that is precisely coaxial with the aerosol plume and of opposite direction to the aerosol plume.
A sixth object of the present disclosure is to provide heated compressed gas to both the nozzle and the counter-flow tube while minimizing heat losses.
A seventh object of the present disclosure is to provide, from a source outside the evaporation chamber, localized radiant heat to the newly formed aqueous aerosol particles at the wavelength of the maximum infrared absorption for water.
An eighth object of the present disclosure is to allow the device to be used with different easily interchangeable nozzle-holder configurations that enable compressed gas either to be delivered through a central orifice or surround a central fluid stream.
A ninth object of the present disclosure is to have these nozzle-holders keyed for use in the flow conditioner and to have the ability to include a compressible fluid reservoir in place of a fluid inlet.
A tenth object of the present disclosure is, in a compact device, to provide for a high velocity gas stream to be heated while it flows in one direction and then provide a uniform lower velocity flow in the opposite direction while allowing for the perturbations caused by an aerosol plume and counter-flow gas.
An eleventh object of the present disclosure is to efficiently concentrate a respirable aerosol larger than 0.5 micron with minimal pressure drop between the input and the exhaust gas.
A twelfth object of the present disclosure is to facilitate easy assembly and disassembly while maintaining axial and rotational high precision alignment.
A thirteenth object of the present disclosure is to prevent any aerosol particles in the concentrator exhaust gas stream from contaminating the atmosphere.
A fourteenth object of the present disclosure is to minimize any aerosol deposition due to turbulence at the output of the concentrator.
A fifteenth object of the present disclosure is to provide an efficient means of delivering the concentrated aerosol at the output by means of the parabolic shaped nature of the output cone.
A sixteenth object of the present disclosure is to provide a concentrated aerosol at a small positive pressure to provide a pressure-assist for patients who have trouble generating sufficient inspiratory pressure and flow to trigger some other dry powder inhalers.